How much do you plan to offroad the truck and how attached are you to the truck?

Theres lots of work involved just in the axle/spring placement, setting up the steering, aligning and supporting the transfer case, swap transmissions, have driveshafts made, install the transfer case computer (depending on the year truck you have).
If your not a skilled builder this would be a huge undertaking and would take months of work, or lots of $$ if you let a shop do the work.

Two recomendations:

Sell you present truck and buy a 4x4. Usually the least expensive route.
Or
Buy a wrecked 4x4 with a good frame and drivetrain and swap your body on to it. This particular swap could be done much easier than trying to build a 2x4 into a 4x4 and if you shop around for the wrecked donor you can usually get a good price.

I've built 4x4's from 2x4's, swapped 2x4 bodies to 4x4 chassis, and built a few 4x4's from the ground up, by far the easiest is to buy a good running 4x4, the next best method is to replace a wrecked body with your good body on a 4x4 chassis.

go west tons of them - this is alot of work for the back yard mechanic---i done a few as well---- much easier to sell current and get what you want----the dmv paperwork can be a pain to swap motors and bodies since the vin is on the body parts as well as the frame....but it is your money and time so do as you wish and post pictures so others can follow along and see if they wish to follow you...mike